New method to calculate solar irradiation on rear side of bifacial panels


A group of researchers from Turkey’s Middle East Technical University (METU) and Gumushane University have developed a new way to calculate the solar irradiation on the rear side of bifacial solar modules.

The scientists said that the technique can be applied to any kind of PV project or site conditions, without the need for high computational power.

They presented their findings in “Solar irradiation on the rear surface of bifacial solar modules: a modeling approach,” which was recently published in Scientific Reports. The new technique is a modified version of the isotropic diffuse model, which is also known as the Liu and Jordan model. It assumes that diffuse radiance is uniformly distributed.

They started to modify the model by treating the rear side as the front side. They did this by taking the complementary angle of the tilt angle as the real tilt angle. “This correction contributes to the ground reflected irradiation component higher than the one in the original version as expected,” the scientists said.

The second modification involved altering the ratio of beam irradiation on the rear side of the bifacial panels. “The beam contribution on the rear surface is due to the symmetry of the path of the Sun,” the academics explained. “There is only beam contribution on the rear surface for the sunrise and the sunset hours.”

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They performed calculations for the period between sunrise and sunset. The PVForm algorithms, developed by Sandia National Laboratories in the United States, were used to calculate the power yield of bifacial modules through the proposed approach.

The researchers said the difference between irradiation on the bottom, middle, and top parts of the panel’s rear side was crucial in the modeling approach. The model was tested via two different statistical models – the mean bias error and the root mean square error.

“To make the verification of the model more comprehensive, the annual energy yield of the bifacial PV module is estimated,” the researchers said. “The results showed that estimated and measured rear side solar irradiance values agree quite well.”

They claimed that the rear side of the panels receive more light on the top and bottom back, while the middle part receives less light due to shading. The method is said to work well on both sunny and cloudy days.

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